In the art are known exhaust gas treatment systems for the emissions reduction and in particular of particulates and oxides of nitrogen (NOX) from the diesel engine exhaust gas. These systems are provided with after-treatment devices installed along the exhaust line of the engine. The selective catalytic reduction (SCR) system is one of the used after-treatment system for NOX control.
It is also known in the art, in some exhaust system configuration, to inject a reagent (catalyst) fluid in the exhaust line of the diesel engine in order to reduce emissions by means of the afore-mentioned after-treatment devices. In particular, a fluid catalyst such as urea, or ammonia, or a combination thereof (generally in a water solution) are injected into the exhaust line of the diesel engine in order to promote the reduction of nitrogen oxides (NOX) in the SCR. The SCR system includes an additional tank into the vehicle platform containing the diesel exhaust fluid or DEF. DEF freezes in cold condition according to the liquid characteristic (for example, one of the most used, the so called Adblue, freezes at −11° C.). It is important in cold conditions to have the liquid thermal state estimation (i.e. 100% solid phase, 100% liquid phase or a mixture of solid phase and liquid phase) and to calculate also the total amount of defrosted DEF to guarantee that SCR system works in those conditions in a proper way and according to the legislative requirements.
In fact, for SCR applications, the thermal state estimation of the DEF, which is contained in the tank, is needed to better manage the SCR control in cold condition. Typically, the amount of liquid inside a frozen tank with heating function is an important parameter: in SCR systems the DEF is injected to reduce NOx emission and in cold conditions the available DEF information is needed to be sure that the system works as well as possible. Without this information, it means the system can inject all the available DEF. Consequently, the hydraulic system cannot work properly and damaging of the hardware has to be expected.
DE 102011106552 A1 discloses that if the diesel exhaust fluid is at least partially frozen, then a temporary minimum diesel exhaust fluid mass may be defined. US 20110047966 A1 discloses an apparatus for controlling the heating of diesel exhaust fluid in a DEF delivery system which includes a temperature comparison module that compares a difference between a sensed ambient air temperature and a sensed DEF tank temperature with a predetermined temperature difference threshold.
There is a need in the art to provide a method and an apparatus which estimates the thermal state or the thermal state transition of a substance, which can be a 100% solid phase or a 100% liquid phase or a mixture of solid phase and liquid phase, or in other words the substance can be totally frozen, partially frozen, or totally liquid.